This topic presents in a very simplified way all the main concepts that should be understood by those who know 5G NR.
5G NR UE Identities
In 5G NR, UE identities ensure secure, efficient, and flexible user and device management while improving on LTE capabilities. The IMSI, a globally unique subscriber identity also used in LTE, is now better protected in 5G through encryption when used in signaling. The IMEI, a permanent device-specific identifier, remains unencrypted and supports device-level management similar to LTE. 5G introduces the SUPI (replacing IMSI for signaling) and its encrypted counterpart, the SUCI, to safeguard subscriber identities during transmission, a major privacy improvement over LTE. Temporary identifiers like the 5G-GUTI (a dynamic identity for mobility and privacy) and its streamlined version, the 5G-S-TMSI, enhance signaling efficiency and adapt to interworking with LTE via mapping to the 4G GUTI. Additionally, 5G redefines RNTIs, such as the C-RNTI for individual UEs and INT-RNTI for group tasks, to address devices dynamically in the Radio Access Network. The I-RNTI, unique to 5G, supports inactive state management by enabling efficient paging and signaling without payload scrambling. These enhancements reflect 5G’s focus on privacy, efficiency, and seamless mobility compared to LTE. [In a Nutshell: 5G improves on LTE by introducing secure, temporary, and task-specific identifiers to enhance privacy, efficiency, and seamless connectivity.]
Imagine two cities, LTE City and 5G City. In LTE City, everyone walks around with their name tags visible (IMSI), and each house has a permanent number (IMEI) painted on it. While this works, it’s not very safe because anyone can see who you are. In 5G City, things are much smarter - people wear secret badges (SUPI), and when they leave their house, the badge is covered by a special lock (SUCI) that hides their real name, keeping them safe. In both cities, temporary nicknames (like 5G-GUTI and 5G-S-TMSI in 5G City) are used to call out to people when needed, but 5G City has better, faster ways to find and talk to its citizens. Even for big group announcements or when someone is taking a nap (I-RNTI for inactive people), 5G City has clever systems to make sure everyone is reached. It’s like 5G City learned all of LTE City’s tricks and added super-smart tools to make everything safer and faster! [In a Nutshell: 5G City is like LTE City but with secret badges, locks, and smarter tools for safer and faster communication.]
5G NR UE Identities in a 5G City, as people wearing secret badges (SUPI) covered by locks (SUCI) when outdoors for privacy. Signs displaying temporary nicknames (5G-GUTI and 5G-S-TMSI) are used for calling people efficiently. A person napping represents the I-RNTI for inactive state management.
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IMSI
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The International Mobile Subscriber Identity (IMSI) is a unique identifier that links a mobile user to their network and is stored on the SIM card (or USIM in 5G) and the core network. Like in LTE, it includes three parts: the Mobile Country Code (MCC), Mobile Network Code (MNC), and Mobile Subscriber Identification Number (MSIN), which together identify the user’s home network and specific subscription. While LTE uses the IMSI for signaling and paging, 5G enhances privacy by encrypting the IMSI during signaling and replacing it with temporary identifiers in many processes, including paging, to protect user identity. This ensures security and privacy improvements in 5G compared to LTE. [In a Nutshell: 5G encrypts and replaces IMSI with temporary IDs to protect user identity and improve privacy over LTE.]
The International Mobile Subscriber Identity (IMSI) acts like a secret passport that connects a mobile user to their home network, stored on the SIM card (USIM in 5G) and the core network. It’s made up of three parts: the country code (MCC), the network code (MNC), and a unique subscriber number (MSIN), much like in LTE. While LTE often uses this passport directly for tasks like signaling and paging, 5G enhances security by encrypting the IMSI during communication and using temporary IDs for many tasks, including paging. This protects the user’s identity and makes 5G more private and secure than LTE. [In a Nutshell: IMSI is like a secret passport in 5G, encrypted for better privacy and security compared to LTE.]
5G NR IMSI as a device holding a ‘secret passport’ (representing the IMSI) with visible encryption locks around it. The passport shows three parts labeled MCC, MNC, and MSIN. In the background, 5G infrastructure like antennas and core network buildings is visible, with glowing secure links (temporary IDs) replacing direct IMSI usage for signaling.
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5G NR IMSI 
IMEI
The International Mobile Equipment Identity (IMEI) is a unique, permanent identifier for mobile devices, stored in the hardware and the network core. Like LTE, the IMEI in 5G is structured with three parts: the Type Allocation Code (TAC), which identifies the device model and version; the Serial Number (SNR), which uniquely distinguishes individual devices of the same model; and the Check Digit (CD), used to detect data entry errors. Unlike the IMSI, the IMEI is not encrypted in signaling and is used to identify devices rather than subscribers, serving as a critical tool for managing device access and security across networks. [In a Nutshell: IMEI is a permanent “device ID” used for access and security, unchanged from LTE to 5G, and not tied to user identity.]
The International Mobile Equipment Identity (IMEI) is like a permanent license plate for mobile devices, stored in the device hardware and network core. Just like in LTE, the IMEI in 5G is divided into three parts: the Type Allocation Code (TAC), identifying the device’s model and version; the Serial Number (SNR), distinguishing individual devices of the same model; and the Check Digit (CD), which helps catch input errors. Unlike the IMSI, the IMEI isn’t encrypted and focuses on identifying the device itself rather than the user, making it essential for managing access and ensuring security across mobile networks. [In a Nutshell: IMEI is the device’s license plate, helping manage and secure devices without tying it to the user.]
5G NR IMEI as a device holding a ‘permanent license plate’ (representing the IMEI) with three visible sections labeled TAC, SNR, and CD. The license plate is detailed and permanent, emphasizing its role as a unique device identifier. In the background, 5G infrastructure such as antennas, core network buildings, and secure devices are visible, symbolizing device management and security.
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SUPI & SUCI
In 5G, the Subscription Permanent Identifier (SUPI) uniquely identifies a subscriber and can either be an IMSI (used in LTE) or a Network Access Identifier (NAI) specific to private networks, formatted like an email address (username@realm). To enhance privacy, 5G introduces the Subscription Concealed Identifier (SUCI), which encrypts the SUPI during signaling to prevent user identity exposure. The SUCI is derived using protection schemes, such as ECIES profiles or operator-specific methods, and replaces the SUPI in signaling, making 5G more secure than LTE by protecting subscriber identities during communication. [In a Nutshell: SUPI is a subscriber ID in 5G that’s encrypted as SUCI to improve privacy and protect user identity, unlike LTE.]
In 5G, the Subscription Permanent Identifier (SUPI) is like a unique membership card for mobile users, identifying them to the network. It can either be the traditional IMSI, as in LTE, or a special Network Access Identifier (NAI) for private networks, resembling an email address (username@realm). To keep user identities private, 5G introduces the Subscription Concealed Identifier (SUCI), which acts like a locked version of the membership card. The SUCI encrypts the SUPI during communication, using advanced protection methods like ECIES profiles, ensuring that personal details remain hidden. This enhancement makes 5G much more secure than LTE by safeguarding subscriber identities. [In a Nutshell: SUPI is like a private membership card in 5G, locked as SUCI to ensure user privacy and enhance security compared to LTE.]
5G NR - SUPI & SUCI as a device holding a ‘membership card’ (representing the SUPI), which is visibly encrypted with a secure lock symbol (representing the SUCI). The membership card has two formats displayed: a traditional IMSI and an email-like NAI format (username@realm). In the background, 5G infrastructure like antennas and core network buildings is visible, emphasizing advanced security measures and glowing encrypted connections.
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5G-GUTI
The 5G Globally Unique Temporary Identifier (5G-GUTI) is a temporary identifier assigned by the Access and Mobility Management Function (AMF) in the 5G Core Network, designed to enhance user privacy by avoiding the use of permanent identities like the IMSI. It consists of two main components: the Globally Unique AMF Identifier (GUAMI), which specifies the AMF and includes details like the MCC, MNC, and AMF-specific identities, and the 5G-TMSI, which uniquely identifies the UE within that AMF. A critical feature of 5G-GUTI is its mapping to and from the 4G GUTI to ensure seamless handover between 4G and 5G networks. This mapping allows devices to transition between technologies while maintaining their context, ensuring efficient communication continuity. [In a Nutshell: 5G-GUTI is a privacy-focused temporary ID enabling seamless handovers and efficient mobility between 4G and 5G networks.]
The 5G Globally Unique Temporary Identifier (5G-GUTI) is like a temporary nickname given to mobile devices by the Access and Mobility Management Function (AMF) in the 5G Core Network. This nickname helps keep users’ real identities, like the IMSI, private. It consists of two parts: the Globally Unique AMF Identifier (GUAMI), which identifies the AMF and includes network details like country and network codes, and the 5G-TMSI, which uniquely identifies the device within the AMF. A standout feature of 5G-GUTI is its ability to translate back and forth with the 4G GUTI, ensuring a smooth handover between 4G and 5G networks. This ability to transition while preserving the device’s context makes 5G-GUTI essential for efficient and secure mobility in 5G. [In a Nutshell: 5G-GUTI is a temporary nickname for devices, enabling privacy and smooth transitions between 4G and 5G.]
5G NR 5G-GUTI as a device wearing a badge with a ‘temporary nickname’ (representing the 5G-GUTI), which includes two visible parts: the GUAMI (labeled with MCC, MNC, and AMF identifiers) and the 5G-TMSI (a unique device identifier). Another smaller badge labeled ‘4G GUTI’ is shown nearby, symbolizing the seamless transition between 4G and 5G networks. The background features 5G infrastructure like antennas and core network elements with glowing lines representing efficient and private communication.
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5G-S-TMSI
The 5G Short Temporary Mobile Subscriber Identity (5G-S-TMSI) is a streamlined version of the 5G-GUTI, excluding broader identifiers like the PLMN and AMF Region Identity. This makes it suitable for identifying a UE within a specific AMF Region while reducing signaling overhead. Its compact size (48 bits) ensures efficiency in signaling, such as during RRC procedures, where parts of the 5G-S-TMSI are included in setup and completion messages. Additionally, it is used in Paging messages, making it a key tool for quick and resource-efficient communication within 5G networks. This efficiency improvement contrasts with LTE, which relies on larger identifiers. [In a Nutshell: 5G-S-TMSI is a compact, efficient temporary ID for signaling and paging, improving on LTE’s larger identifiers.]
The 5G Short Temporary Mobile Subscriber Identity (5G-S-TMSI) is like a shorthand version of the 5G-GUTI, focusing only on what’s needed to identify a device within a specific AMF Region. By leaving out broader details like the PLMN and AMF Region Identity, it becomes smaller (48 bits), making it quicker and more efficient for tasks like setup, completion, and Paging messages. This streamlined design reduces signaling overhead, ensuring faster communication within 5G networks. Unlike LTE, which uses larger identifiers, the 5G-S-TMSI optimizes efficiency for modern network demands. [In a Nutshell: 5G-S-TMSI is a short, efficient ID for faster communication and less signaling in 5G, improving over LTE.]
5G NR 5G-S-TMSI as a device holding a compact ‘shorthand badge’ (representing the 5G-S-TMSI) with simplified details, emphasizing its small size (48 bits). The badge is visibly smaller compared to a full-size 5G-GUTI badge displayed nearby, showing how 5G-S-TMSI omits broader identifiers like PLMN and AMF Region Identity. The background features 5G infrastructure, such as antennas and core network buildings, with dynamic glowing lines representing fast and efficient communication during RRC and Paging procedures.
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RNTI
Radio Network Temporary Identifiers (RNTIs) are used in the Radio Access Network to uniquely or collectively address devices for various communication tasks. These 16-bit identifiers, allocated by the base station, enable efficient signaling by scrambling payloads on control channels and directing resources like uplink/downlink allocations, power control commands, or system updates. Different RNTI types serve specific purposes: for example, the C-RNTI identifies individual devices, while the SI-RNTI addresses all devices. Specialized RNTIs, such as the TPC-RNTI, manage power control, while the INT-RNTI signals pre-emption for prioritized tasks. Additionally, the RA-RNTI is used in the Random Access process, and the SFI-RNTI dynamically adjusts slot formats. These identifiers streamline operations by ensuring precise addressing, resource allocation, and efficient signaling across devices, providing a flexible and scalable communication framework in 5G networks. [In a Nutshell: RNTIs are 16-bit tags in 5G for efficient device communication, covering tasks from addressing to resource management, improving flexibility and scalability.]
Radio Network Temporary Identifiers (RNTIs) are like special tags assigned by the base station in 5G networks to help manage and communicate with devices efficiently. These 16-bit tags are used for specific tasks: the C-RNTI acts like a personal tag for individual devices, the SI-RNTI broadcasts to all devices, and others like the TPC-RNTI handle power adjustments or the INT-RNTI manage urgent tasks. Some, like the RA-RNTI, help during device connection setup, while the SFI-RNTI adapts time slots for communication. By using these versatile identifiers, 5G ensures precise, scalable, and efficient network operations, improving on LTE’s capabilities. [In a Nutshell: RNTIs are special tags in 5G for managing communication, addressing, and tasks efficiently, enhancing LTE’s network operations.]
5G NR RNTI as a device wearing multiple ‘special tags’ (representing the RNTIs), each labeled with their specific roles: C-RNTI (personal tag), SI-RNTI (broadcast tag), TPC-RNTI (power control), INT-RNTI (urgent tasks), RA-RNTI (connection setup), and SFI-RNTI (slot adaptation). Each tag is visually distinct to highlight its unique function. In the background, a 5G network infrastructure with antennas and control panels showcases resource allocation and signaling tasks. Dynamic glowing lines symbolize efficient and precise communication within the network.
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I-RNTI
The Inactive RNTI (I-RNTI) is a unique identifier used in 5G to manage devices in the RRC Inactive state, allowing efficient signaling without scrambling payloads on control channels. It helps identify both the UE and the Base Station hosting its context, enabling seamless handovers if the UE moves while inactive. There are two versions: a full I-RNTI (40 bits), used in scenarios requiring larger messages but with potential coverage risks, and a short I-RNTI (24 bits), optimized for standard messaging. The choice between these depends on the useFullResumeID flag in system information. While 3GPP doesn’t mandate how bits are divided between identifying the Base Station and UE, the I-RNTI supports efficient paging and connection resumption, enhancing resource management for idle devices in 5G networks. [In a Nutshell: I-RNTI is an efficient identifier for managing inactive devices in 5G, enabling seamless handovers and resource optimization.]
The Inactive RNTI (I-RNTI) is like a temporary parking ticket assigned to devices in the RRC Inactive state in 5G, allowing them to be located and managed efficiently without extra signaling complexity. It identifies both the device and the base station hosting its context, ensuring smooth transitions if the device moves. There are two versions: a full I-RNTI (40 bits) for larger, more detailed tasks and a short I-RNTI (24 bits) for standard use, chosen based on the useFullResumeID flag. While the exact division of bits is flexible, the I-RNTI ensures seamless paging and quick reconnections, making 5G resource management more efficient than LTE. [In a Nutshell: I-RNTI is a temporary ticket in 5G for inactive devices, enabling smooth transitions and efficient resource use.]
5G NR - I-RNTI as device holding a ‘temporary parking ticket’ (representing the I-RNTI). There are two versions: a full I-RNTI (40 bits) for larger tasks and a short I-RNTI (24 bits) for standard use. The parking ticket also symbolizes seamless handovers and efficient paging. In the background, 5G infrastructure, such as antennas and base stations, is depicted, emphasizing efficient signaling and resource optimization for idle devices.
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Quick Summary
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IMSI: uniquely identifies mobile users. In 5G, it’s encrypted and replaced with temporary IDs for better privacy than LTE. (5G NR IMSI is like a ‘secret passport’ with encryption locks (MCC, MNC, MSIN), secure links replace direct usage in signaling.)
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IMEI: is a permanent device ID (TAC, SNR, CD) for access and security, unchanged from LTE to 5G, not linked to user identity. (5G NR IMEI is like a ‘permanent license plate’ (TAC, SNR, CD), uniquely identifying devices, with 5G infrastructure highlighting security and management.)
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SUPI & SUCI: SUPI is a 5G subscriber ID encrypted as SUCI for enhanced privacy, protecting user identity during communication. (SUPI is like a ‘membership card’ (IMSI/NAI) encrypted as SUCI for advanced security and encrypted connections.)
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5G-GUTI: is a privacy-focused temporary ID enabling seamless 4G-5G handovers and efficient mobility. (Like a ‘temporary nickname’ badge (GUAMI and 5G-TMSI), with a nearby ‘4G GUTI’ badge, symbolizing seamless 4G-5G transitions and private communication.)
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5G-S-TMSI: is a compact, efficient temporary ID for signaling and paging, optimizing communication over LTE’s larger identifiers. (Like a ‘shorthand badge’ (48 bits), smaller than 5G-GUTI, for fast, efficient RRC and Paging within 5G networks.)
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RNTI: are 16-bit tags in 5G enabling efficient communication, resource management, and flexible operations across devices. (Like ‘special tags’ (C-RNTI, SI-RNTI, etc.), highlighting distinct roles for efficient and precise 5G communication.)
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I-RNTI: is an efficient 5G identifier for managing inactive devices, supporting seamless handovers and resource optimization. (Like a ‘parking ticket’ (40-bit and 24-bit versions), enabling seamless handovers, efficient paging, and resource optimization.)
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